/Engine/Source/Runtime/NetworkReplayStreaming/LocalFileNetworkReplayStreaming/Public/LocalFileNetworkReplayStreaming.h
Returns a name formatted as "demoX", where X is between 1 and MAX_DEMOS, inclusive. Returns the first value that doesn't yet exist, or if they all exist, returns the oldest one (it will be overwritten).
[FString](API\Runtime\Core\Containers\FString) GetAutomaticDemoName() const